1. Q: Why do galvanized color-coated coils need a back coating?
A: The main purpose is for corrosion protection on the back. The front of the color-coated coil is a decorative topcoat, while the back (the side in direct contact with the zinc layer of the substrate) is frequently exposed to humid air, insulation materials, or condensation during use. The back coating forms a protective layer, preventing the zinc layer from corroding, developing white rust, or turning black, thus extending the overall service life.
2. Q: Does the back coating increase adhesion to the core material?
A: Yes. When color-coated coils are used in composite panels (such as polyurethane, rock wool, and EPS sandwich panels), the back coating needs to have good adhesion and compatibility with the foaming material. Some back coatings are designed as chemically modified coatings that can react with foaming materials such as polyurethane to prevent delamination and blistering.
3. Q: Does the back coating prevent scratches during transportation and processing?
A: It provides basic protection. The back coating has a certain degree of hardness and abrasion resistance, which can reduce mechanical damage to the zinc layer on the back side during interlayer friction of the steel coil, uncoiling, and molding. However, the back coating is usually thinner than the front coating (about 5~10μm), and its main function is corrosion protection rather than protection against severe scratches.
4. Q: How to choose the color and thickness of the backing paint?
A: Backing paint is usually gray, white, light yellow, or transparent, making it easy for users to identify whether the coating is intact. Standard thicknesses:
General anti-corrosion type: 5~8μm
Composite board type: 8~12μm (adhesion must also be considered)
High weather resistance environments (such as chemical plants, seaside): can be thickened to over 15μm.
Color usually does not affect performance, but white backing paint is easier to detect in cases of roof perforations and leaks.
5. Q: Can galvanized color-coated coils without a backing paint be used?
A: Only for short-term, temporary use in dry indoor environments. Without a backing paint, the zinc layer is directly exposed to moisture, acids, alkalis, or comes into contact with wood (acidic) or cement (alkaline), which may cause white rust and black spots to appear within weeks to months, thus compromising the adhesion of the topcoat. Formal projects require double-sided coating (at least an epoxy or polyester primer for the backing paint).